Health monitoring for power converter capacitors

ABSTRACT

A method for detecting a performance degradation of a capacitor in a power converter is disclosed. The method includes monitoring a voltage across the capacitor, detecting the performance degradation of the capacitor based on the monitored voltage, and generating a warning signal after detecting the performance degradation of the capacitor. A power converter is including at least one capacitor and a processor operably coupled to the at least one capacitor for monitoring a voltage across the at least one capacitor is also disclosed. The processor is configured for detecting a performance degradation of the capacitor based, at least in part, on the monitored voltage, and for generating a warning signal after detecting the performance degradation of the at least one capacitor.

FIELD

The present disclosure relates to power converters including AC/DC andDC/DC power converters.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A wide variety of power converters are known in the art for convertingelectric power from one form to another, including AC/DC and DC/DC powerconverters. These power converters commonly include one or morecontrollers that, among other things, monitor critical parameters suchas input current, output current and/or temperature. When an overcurrentor over-temperature condition is detected, the controller can generate afault signal and/or shutdown the power converter to prevent or minimizedamage to the power converter and any system hosting the power converter(e.g., a computer or automotive system). Although these known approachesare useful for detecting faults, the present inventors have recognized aneed for further improvements in power supply fault detection.

SUMMARY

According to one aspect of the present disclosure, a method fordetecting a performance degradation of a capacitor in a power converteris disclosed. The method includes monitoring a voltage across thecapacitor, detecting the performance degradation of the capacitor basedon the monitored voltage, and generating a warning signal afterdetecting the performance degradation of the capacitor.

According to another aspect of the present disclosure, a power converterincludes at least one capacitor and a processor operably coupled to theat least one capacitor for monitoring a voltage across the at least onecapacitor. The processor is configured for detecting a performancedegradation of the capacitor based, at least in part, on the monitoredvoltage, and for generating a warning signal after detecting theperformance degradation of the at least one capacitor.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a flow diagram of a method of monitoring a performancecharacteristic of a power converter to determine the health of acomponent in the power converter.

FIG. 2 is a block diagram of a power converter configured to monitor thehealth of one or more components in the power converter.

FIG. 3 is a block diagram of a power converter configured to monitor thehealth of a bulk capacitor, an output capacitor and a dc fan.

FIG. 4 is a is a graph relating ripple voltage to the duty cycle of aPWM signal.

FIG. 5 is a flow diagram of a process for monitoring the health of abulk capacitor in a power converter.

FIGS. 6 and 7 are schematic diagrams of sample bulk capacitor ripplevoltage detection circuits.

FIG. 8 is a flow diagram of a process for monitoring the health of anoutput capacitor in a power converter.

FIG. 9 is a schematic diagram of an output capacitor ripple voltagedetection circuit.

FIG. 10 is a flow diagram of a process for monitoring the health of a dcfan in a power converter.

FIG. 11 is a flow diagram of a process for monitoring the health of anelectric motor.

FIG. 12 is a flow diagram of a capture interrupt service processperformed by the processor shown in FIG. 3.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

A method for monitoring the health of at least one component in a powerconverter according to one aspect of the present disclosure isillustrated in FIG. 1 and indicated generally by reference number 100.As shown in FIG. 1, the method 100 includes, at 102, monitoring at leastone performance characteristic of the power converter which relates tothe health of the component. At 104, the monitored performancecharacteristic is compared with stored data to determine whether thehealth of the component has reached a predetermined level. At 106, awarning signal is generated after determining the health of thecomponent has reached the predetermined level. In this manner, adegradation in the health of one or more power supply components can bedetected and reported so as to permit timely service (ranging from minormaintenance to replacement) of such component(s) prior to a completefailure of the component(s) and/or the power converter. These teachingscan be applied to AC/DC and DC/DC power converters, includingswitch-mode power supplies.

In some embodiments, the health of multiple components of a powerconverter are monitored. Preferably, each monitored component isassociated with a unique warning signal that is generated when thehealth of that component has degraded to a predetermined level. In thismanner, the generated warning signal identifies the particular componentin need of service or replacement. Alternatively, the same warningsignal can be generated when the health of any one of the components hasdegraded to a particular level.

Further, in some embodiments, one or more alarms are provided andactivated by the generated warning signal(s) so as to provide a visualand/or audible warning when a component is in need of service.Additionally, or in the alternative, the generated warning signal(s) canbe provided to a load supplied by the power converter, including to aprocessor in a system hosting the power converter (such as a computerserver). The power converter can also be configured to shut down aftergenerating a particular warning signal.

With further reference to the method 100 of FIG. 1, the particularcomponent whose health is monitored can be, for example, a capacitor, afan or any other critical performance component of the power converter.In the case of an electrolytic capacitor, the ripple voltage across thecapacitor can be used to represent the health of the capacitor, and cantherefore be monitored to determine whether the health of the capacitorhas degraded to a particular level. In particular, as the electrolyte ofa capacitor decreases gradually over time, the effective seriesresistance of the capacitor increases and its capacitance decreases,which leads to greater and greater ripple voltage. Accordingly, ripplevoltage can be used as an indicator of the capacitor's health. In thecase of a fan, the fan speed for a given load, control input and/ortemperature condition can be used to represent the health of the fan.Thus, the health of a power converter fan can be monitored bymonitoring, e.g., fan speed, fan speed commands, temperature and/oroutput current level.

FIG. 2 illustrates a power converter 200 according to one embodiment ofthe present disclosure. The power converter 200 includes a processor 202and various components 204, 206, 208 whose performance in the powerconverter will degrade over time (e.g., due to wear out, decay, thermalcycling, etc.). The power converter 200 further includes alarms 210,212, 214. The processor 202 is configured to monitor the health of thecomponents 204, 206, 208 over time. When the monitored performance ofany of these components reaches a threshold level, the processor 202activates the corresponding alarm 204, 206 or 208. In the specificembodiment of FIG. 2, each monitored component 204, 206, 208 isassociated with a different alarm 210, 212, 214, respectively. In thismanner, a user can readily determine which component is in need ofservice based on which alarm is activated.

The alarms shown in FIG. 2 can be visual alarms and/or audible alarms.In the case of visual alarms, one or more lights (including lightemitting diodes (LEDs)) can be employed, as can display devices fordisplaying text or other messages (e.g., icons), etc. If the alarmincludes one or more lights, activating the alarm can include turning iton, turning it off, causing it to flash or blink at a particular rate,changing its color, etc. In some embodiments, each alarm includes an LEDhaving a different color than the LEDs of other alarms. In this manner,a user can readily identify when a particular component is in need ofservice based on the color of the activated LED.

As an alternative, or in addition to, providing audible and/or visualalarms, a component status log can be generated and stored. Thecomponent status log can be accessed to retrieve historical dataregarding the status of components of the power supply. Additionally,the alarm may include an alarm signal communicated between the powerconverter 200 and a host system of the power converter 200.

The processor 202 of FIG. 2 can be configured to monitor the health ofcomponents 204, 206, 208 using the method 100 of FIG. 1 or any othersuitable method. Further, while the processor 202 shown in FIG. 2 isconfigured for monitoring the health of three components, it should beappreciated that more or less than three components can be monitored inany given implementation. Similarly, the number of alarms employed canbe more or less than three, and may be as few as one. The processor 202shown in FIG. 2 (and FIG. 3) may be a digital controller such as amicroprocessor, a microcontroller, a microcomputer, a digital signalprocessor, etc. or any other suitable processing device. The processor202 may be a dedicated processor or may be a processor that performsother, possibly unrelated, functions within the power supply. Theprocessor 202 may be implemented using a combination of hardware,software and firmware. Alternatively, the processor 202 may beimplemented using a hardwired analog and/or digital circuit.

FIG. 3 illustrates a power converter 300 according to another embodimentof this disclosure. As shown in FIG. 3, the power converter 300 includesan electrolytic bulk capacitor 302, an electrolytic output capacitor316, and a dc fan 304. The performance of these components will degradeover time. The power converter also includes a processor 306 formonitoring the health of the bulk capacitor 302, the output capacitor316 and the fan 304 using the method 100 of FIG. 1. The power converter300 may be configured as an AC/DC or DC/DC power converter. The powerconverter 300 can also include a power factor correction input stage(not shown).

More specifically, the processor 306 monitors the health of the bulkcapacitor 302 and the output capacitor 316 by monitoring the ripplevoltage across these devices and the output current level. For thispurpose, the power converter 300 includes two ripple voltage samplingcircuits 312 and 314 and an output current sampling circuit 310. Theprocessor monitors the health of the dc fan 304 by monitoring the fanspeed and the temperature of a heat sink (not shown) associated with thefan. For this purpose, the power converter includes a temperaturesensing circuit 308 and the processor includes an input for monitoring afan speed signal 317. These various circuits provide data to theprocessor 306. As further described below, this data is used by theprocessor to determine whether the health of any monitored component hasdegraded to a predetermined threshold level.

In the particular embodiment of FIG. 3, the processor 306 is configuredto generate different warning signals 318, 320, 322 based on whichcomponent is in need of service. These warning signals are used toactivate corresponding LEDs 324, 326, 328, with each LED having adifferent color. Once a particular LED is activated, a user can scheduleappropriate service of the power converter before the component iscompletely damaged.

In the particular embodiment of FIG. 3, the ripple voltage across thebulk capacitor is detected and converted to a pulse width modulated(PWM) signal having a duty cycle. The duty cycle of the PWM signalcorresponds to the peak-to-peak magnitude of the detected ripplevoltage. The greater the ripple voltage, the greater the duty cycle ofthe PWM signal. This relationship between the ripple voltage and theduty cycle of the PWM signal is illustrated in FIG. 4. As shown therein,the largest ripple voltage 402 corresponds to the PWM signal 412 withthe largest duty cycle. A second and smaller ripple voltage 404corresponds to a PWM signal 414 with a smaller duty cycle. The smallestripple voltage 406 shown in FIG. 4 corresponds to the PWM signal 416with the smallest duty cycle. In this manner, the processor 306 receivesa PWM signal from the ripple sampling circuit 314 (preferably via anisolation device such as an optical coupler), with the duty cycle of thePWM signal representing the ripple voltage detected across the bulkcapacitor 302.

By comparing the ripple voltage detected across the bulk capacitor 302,and comparing this information to stored data, the processor 306 candetermine whether the health of the bulk capacitor has degraded to athreshold level indicating a need for service. In some embodiments, thisthreshold level is selected as a percentage (e.g., 20%) increase in thenormal (initial) bulk capacitor ripple voltage. Thus, the processor 306can be configured to generate the warning signal 318 (indicating a needto service the bulk capacitor) when the ripple voltage detected acrossthe bulk capacitor 302 exceeds the initial bulk capacitor ripple voltageby more than twenty percent. Alternatively, ripple data associated witha former power supply failure can be stored and used in the detectioncriterion.

In some embodiments, the processor determines the health of the bulkcapacitor 302 as a function of the ripple voltage across the bulkcapacitor at a given output current level. One example of this isillustrated by the flow diagram of FIG. 5. At 502, the processordetermines the duty cycle of the PWM signal generated by the bulkcapacitor ripple voltage sampling circuit 314. At 504, the processordetermines the output current level (as indicated by the currentsampling circuit 310). At 506, the processor determines whether theoutput current is less than or equal to a current level corresponding toa half-load condition. If the current is less than or equal to the halfload current, the processor determines, at 508, whether the duty cycleof the PWM signal (as provided by the ripple sampling circuit 314) isgreater than a duty cycle corresponding to half-load condition. If so,the processor generates a warning signal at 512. Otherwise, processingloops back and repeats. If the processor determines at 506 that theoutput current is greater than the half-load condition, processingproceeds to 510 for determining whether the duty cycle of the PWM signalis greater than a duty cycle corresponding to a full load condition. Ifso, the processor generates a warning signal at 512. Otherwise,processing loops back and repeats. Although the method has beenexplained and illustrated with reference to only two load levels, itshould be understood that the method can also be used with more than twoload levels.

FIGS. 6 and 7 illustrate two examples of bulk capacitor ripple voltagesampling circuits 600, 700 suitable for use in the power converter ofFIG. 3. As shown in FIG. 6, the ripple voltage across the bulk capacitoris provided to the circuit 600 as an input 602. A comparator 604converts the input ripple voltage to a PWM signal having a duty cycle.In the circuit 700 of FIG. 7, a comparator 702 and an opto-coupler 704are employed to achieve results similar to the circuit 600 of FIG. 6. Itshould be understood, however, that a variety of other circuits can beemployed for detecting the ripple voltage across the bulk capacitor 302without departing from the teachings of this disclosure.

With further reference to FIG. 3, the output capacitor ripple voltagesampling circuit 312 provides a signal to the processor 306 representingthe ripple voltage across the output capacitor 316. In the particularembodiment of FIG. 3, this signal provided to the processor represents apeak value of the output capacitor ripple voltage. Alternatively, othersignals can be used so long as there is a known relationship between theripple magnitude and the signal format.

In some embodiments, a ripple voltage signal passes through a peak valuedetection circuit before being input to the processor 306. Powerconverter secondary side ripple voltage often has a frequencyapproximately equivalent to a switching frequency of the power converteror an integer multiple of the switching frequency. Switching frequencyis, in many instances, greater than 100 kHz and may increase in thefuture. Thus the frequency of the ripple voltage is often well in excessof 100 kHz. Computational processing of AC signals at several hundredkHz can be complex and expensive. The complexity and expense can bereduced by converting the ripple voltage AC signal to a DC voltage. Avariety of AC to DC conversion techniques can be used to accomplish thisconversion with various degrees of accuracy and complexity. One examplecircuit that may be used for this purpose is a peak value detectionholding circuit.

By comparing the ripple voltage detected across the output capacitor 316with stored data, the processor 306 can determine whether the health ofthe output capacitor 316 has degraded to a threshold level indicating aneed for service. In some embodiments, this threshold level is selectedas a percentage (e.g., 90%) of the maximum rated output ripple voltage.Thus, the processor 306 can be configured to generate the warning signal320 when, e.g., the ripple voltage detected across the output capacitor316 is greater than or equal to ninety percent of the maximum ratedoutput ripple voltage.

In some embodiments, the processor 306 determines the health of theoutput capacitor 316 as a function of the ripple voltage across theoutput capacitor 316 at a given output current level. One example ofthis is illustrated by the flow diagram of FIG. 8. At 802, the processordetermines the value of the ripple voltage detected by the ripplesampling circuit 312. At 804, the processor determines the outputcurrent level as detected by the current sampling circuit 310. Theprocessor then determines, at 806, whether the output current level isless than a current level corresponding to a half-load condition. If thecurrent is less than or equal to the half load current, the processcontinues to 808. At 808, the processor determines whether the ripplevoltage is larger than the ripple voltage expected for a half loadcondition. If so, processing continues to 812 and a warning signal isgenerated. Otherwise, the process loops and repeats. If the processordetermines at 806 that the output current is greater than the half loadcurrent, the processor will proceed to 810 to determine whether theripple voltage is greater than what is expected for a full loadcondition. If so, processing continues to 812 and a warning signal isgenerated. Otherwise, the process loops and repeats.

FIG. 9 illustrates an output capacitor ripple voltage sampling circuit900 suitable for use in the power converter of FIG. 3. As shown in FIG.9, the output capacitor ripple voltage is provided as an input Vin. Theamplitude of the ripple voltage is amplified and then filtered with abandpass filter to remove low frequency ripple (e.g., below half of aswitching frequency of the power converter) and high frequency ripple(e.g., above 500 kHz) noise at the front end of the operationalamplifier X3. The operational amplifier is preferably high speed so asto attain high gain and linearity. The forward voltage drop of the diodeD1 is compensated by the op amp X2 for performance changes due totemperature variation. The resistor paralleled with the capacitorensures discharge of the capacitor. Therefore, when the amplitude of theinput ripple voltage changes, the signal is amplified. The circuit 900converts the output capacitor ripple voltage to an DC signalrepresenting the peak value of the ripple voltage. If the ripple voltageis a sine wave signal, the DC signal output from the circuit 900 mayrepresent the RMS value of the ripple voltage.

As noted above, the processor 306 of FIG. 3 is configured to monitor thehealth of the dc fan 304 by monitoring the fan speed and the temperatureof an associated heat sink. In general, there is a minimum desired fanspeed for a given temperature. Therefore, if the fan speed is less thana predetermined threshold value at a given temperature, this may beindicative of an impending fan failure and can be used to generate anappropriate warning signal.

One example of a process for detecting a performance degradation of thedc fan is illustrated in FIG. 10. As shown therein, the process beginswith determining the speed of the fan at 1002 and the temperature of anassociated heat sink at 1004. At 1006, the process determines whetherthe temperature is less than a lower limit which, in this particularexample, is 38 degrees Celsius. If so, the process loops and repeats.Otherwise, the process determines at 1008 whether the temperature isbelow a higher limit which, in this particular example, is 59 degreesCelsius. If so, the process continues to determine at 1010 whether thefan speed is less than a minimum expected speed for temperatures below59 degrees Celsius. If not, the process loops and repeats. Otherwise,the fan is not operating as it should and processing continues to 1016and generates a warning signal. If processing determines at 1008 thatthe temperature is above the high temperature, processing continues to1012 to determine whether the temperature has exceeded anover-temperature protection value which, in this example, is 61 degreesCelsius. If so, processing continues to 1018 where over temperatureprotection is initiated. Otherwise, processing continues to 1014 todetermine whether the fan speed is less than a minimum expected speedfor temperatures approaching 61 degrees Celsius which, in thisparticular example, is 14,000 rpm. If so, processing continues to 1016and a warning signal is generated. Otherwise, processing loops andrepeats. Alternatively, the processor 306 can be configured to detectperformance degradations in the fan by monitoring the fan speed at agiven applied voltage and/or airflow impedance. Although two temperaturelevels are illustrated in this particular example, implementation ofthis process is not so limited and any number of temperature levels ofvarying magnitudes may be used.

FIG. 11 illustrates a method of detecting performance degradations in anelectric motor according to another aspect of the present disclosure. Asshown in FIG. 11, the method includes, at 1102, monitoring the speed ofthe motor. At 1104, a performance degradation of the motor is detected.At 1106, a warning signal is generated. The method may also includemonitoring control signals provided to the electric motor, including theapplied voltage or duty cycle. In this manner, the performancedegradation of the motor may be determined based, at least in part, onthe monitored speed of the motor and the control signals provided to themotor. In particular, if the monitored speed of the motor does notcoincide with the control signals provided to the motor, this may beindicative of an impending motor failure or other need for servicing themotor. In response to the warning signal, the motor can be serviced asnecessary or replaced. The electric motor may be part of a larger systemor assembly, including for example a power converter fan.

FIG. 12 illustrates a capture interrupt service process performed by theprocessor of FIG. 3 to determine the speed of the fan and the duty cycleof the PWM signal associated the bulk capacitor ripple voltage. As shownin FIG. 12, these two operating characteristics are capturedindependently using a two capture port. The duty cycle is preferablycaptured by measuring the time difference between a rising edge and afalling edge and the time difference between the falling edge and asubsequent rising edge of the PWM signal associated with the bulkcapacitor ripple voltage. Fan speed is preferably captured by measuringthe time interval between successive rising or successive falling edgesof a fan tachometer signal.

Also shown in FIG. 12 is a single average filter block for providingimproved alarm reliability by removing or reducing signal jitter. Thesingle average filter block achieves this objective using a rollingaverage method. Specifically, an average of a predetermined number ofmeasurements is calculated. When a new measurement is available, theoldest measurement is discarded and the new value becomes a component ofthe average.

It should be noted that the processors 202, 306 shown in FIGS. 2 and 3may be included on the same board or package as other power convertercomponents, and may perform processes in addition to those describedherein (including, for example, control processes for a switch-modepower supply). Alternatively, the processors may be located apart fromother components including, for example, in a system hosting the powerconverter (e.g., a computer server).

Although several aspects of the present disclosure have been describedabove with reference to power converters, it should be understood thatvarious aspects of the present disclosure are not limited to powerconverters and can be applied to a variety of systems and applicationsincluding, without limitation, electric motors, automotive systems, andother types of electronic or electromechanical systems used inautomotive, motor control, or other industries.

By implementing any or all of the teachings described above, a number ofbenefits and advantages can be obtained including improved systemreliability, reduced system down time and elimination and reduction ofredundant components or systems, avoiding unnecessary or prematurereplacement of components or systems, and a reduction in overall systemand operating costs.

1. A method for detecting a performance degradation of a capacitor in apower converter, the method comprising: monitoring a voltage across thecapacitor; detecting the performance degradation of the capacitor basedon the monitored voltage; and generating a warning signal afterdetecting the performance degradation of the capacitor.
 2. The method ofclaim 1 wherein the capacitor is an electrolytic capacitor.
 3. Themethod of claim 2 wherein the capacitor is a bulk capacitor.
 4. Themethod of claim 2 wherein the capacitor is an output capacitor.
 5. Themethod of claim 1 further comprising activating an alarm in response tothe generated warning signal.
 6. The method of claim 1 furthercomprising providing the generated warning signal to a system hostingthe power converter.
 7. The method of claim 1 wherein monitoringincludes monitoring a ripple voltage across the capacitor.
 8. The methodof claim 7 wherein monitoring includes converting the ripple voltage toa PWM signal.
 9. The method of claim 7 wherein monitoring includesconverting the ripple voltage to an rms signal.
 10. The method of claim7 wherein detecting includes detecting when the monitored ripple voltageexceeds a predetermined value.
 11. The method of claim 1 furthercomprising replacing the capacitor in response to the generated warningsignal.
 12. A power converter comprising at least one capacitor and aprocessor operably coupled to the at least one capacitor for monitoringa voltage across the at least one capacitor, the processor configuredfor detecting a performance degradation of the capacitor based, at leastin part, on the monitored voltage, and for generating a warning signalafter detecting the performance degradation of the at least onecapacitor.
 13. The power converter of claim 12 wherein the processor isconfigured for generating the warning signal when the detectedperformance degradation of the at least one capacitor exceeds athreshold level.
 14. The power converter of claim 12 wherein the warningsignal activates an alarm.
 15. The power converter of claim 14 whereinthe alarm is a visible alarm.
 16. The power converter of claim 12further comprising at least one LED, the processor configured forchanging a state of the LED after detecting the performance degradationof the at least one capacitor.
 17. The power converter of claim 12wherein the at least one capacitor is an output capacitor.
 18. The powerconverter of claim 17 wherein the monitored voltage is a ripple voltage.19. The power converter of claim 18 further comprising a ripple samplingcircuit operably connected between the output capacitor and theprocessor, the ripple sampling circuit operable to provide a signalrepresentative of a magnitude of the ripple voltage to the processor.20. The power converter of claim 19 further comprising a currentsampling circuit operably connected between the processor and an outputstage of the power converter, the current sampling circuit operable toprovide a signal representative of an output current to the processor.21. The power converter of claim 20 wherein the processor is configuredfor comparing the ripple voltage and output current signals with storeddata to detect the performance degradation of the output capacitor. 22.The power converter of claim 19 wherein the signal representative of themagnitude of the ripple voltage is an RMS voltage.
 23. The powerconverter of claim 12 wherein the at least one capacitor is a bulkcapacitor.
 24. The power converter of claim 23 wherein the monitoredvoltage is a ripple voltage.
 25. The power converter of claim 24 furthercomprising a ripple sampling circuit operably connected between the bulkcapacitor and the processor, the ripple sampling circuit operable toprovide a signal representative of a magnitude of the ripple voltage tothe processor.
 26. The power converter of claim 25 wherein the signalprovided by the ripple sampling circuit is a PWM signal.
 27. The powerconverter of claim 25 further comprising a current sampling circuitoperably connected between the processor and an output stage of thepower converter, the current sampling circuit operable to provide asignal representative of an output current to the processor.
 28. Thepower converter of claim 27 wherein the processor is configured forcomparing the ripple voltage and output current signals with stored datato detect the performance degradation of the bulk capacitor.